Paper manufacture



Oct. 4, 1932. J. TRAQUAIR ET AL PAPER MANUFACTURE 2 Sheets-Sheet 1 Filed Dec. 29, 1928 [A'VENTUR lMu-Lo 2 Oct. 4, 1932. J. TRAQUAIR ET AL PAPER MANUFACTURE Filed Dec. 29, 1928 2 Sheets-Sheet 2 ml mi Patented Oct. 4, 1932 UNITED STATES PATENT OFFICE JOHN TRAQUAIR AND FRANCIS G. RAWLING, 0F CHILLICOTHE, OHIO, ASSIGNORS To THE MEAD RESEARCH ENGINEERING COMPANY, OF DAYTON,

TION OF OHIO OHIO, A CORPORA- rarnn mauurac'runn Application filed December 29, 1928. serial No. 329,082.

This invention relates to the manufacture of paper and the like from cellulose containing materials, and-particularly to the preparation of pulp to be used in such manufacture.

One of the principal objects of the invention isto provide a method of treating fibrous materials to produce a superior pulp product which may be formed into paper having strength, color and other characteristics superior to the corresponding characteristics 1n paper formed from the same fibrous materials in other generally known ways prevlously used.

Another object of the invehtion is to provide a method of treating hard deciduous wood, such for example as chestnut, to produce a whitepulp product of good color and high strength suitable for the manufacture of high grade paper, such as printing paper.

Another object of the invention is to provide such a method in which material econonly in the consumption of chemicals is effected, and which admits of recovery as byproducts of materials dissolved from the fibrous material, to thereby cut down the waste of the fibrous material which has heretofore been considered unavoidable.

Still anotherobject of the invention is to provide apparatus for carrying out the above method.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and appended claims.

In the drawings in which like characters of reference designate like parts throughout the several views thereof- F ig. 1 is a diagrammatic side elevational view of a portion of a preferred embodiment of apparatus constructed for carrying out the method of this invention;

Fig. 1 is a diagrammatic side elevational View of another portion of the apparatus, Figs. 1 and 1 when placed end to end disclosing the complete apparatus; and

Fig. 2 is a diagrammatic partial side elevational view of a somewhat modified form of apparatus.

The present invention provides a method the fibrous material is first of treating fibrous materials of various kinds, such as various types of wood, straw, fibrous grasses and the like, to produce a finished pulp product, of exceptionally high white color and high strength, with marked economy in the consumption of chemicals, and with yields considerably higher than those heretofore obtained in the manufacture of white pulp with the lmownafid generally used pulping processes. The method of this invention is especially adapted for the treatment of hard deciduous or non-resinous broad-leafed wood, such as a chestnut, oak, gum, and the like, to form a superior white or bleached pulp product In accordance with the method of this invention, subjected to an incomplete digestion with chemical under such conditions of temperature and pressure and of concentration and character of chemical as to loosen and soften the bonding material holding the fibers in their natural associated form, without substantially affecting the cellulose and while maintaining the strength of the fibers. In this chemical treatment, the cooking or digestion, which is effective to soften the bonding material holding the fibers together, is purposely so limited in its effects that any considerable defibering or separating of the fibrous material into its ultimate fibers does not result, and there is a resulting high strength and yield of the ultimate product. The partially digested material is then subjected to a multistage and coordinated chlorination treatment to complete the pulping or disintegration thereof, the chlorination treatment being carried out in such wise as to prevent injury to the cellulose fibers, maintain the high strength of the ultimate product and secure a good yield.

In accordance with this invention, the fibrous material after being cooked and before being chlorinated is'extracted with an alkaline liquor, this effecting a material economy in the consumption of the chlorinating agent in the subsequent chlorination treatment Without deleteriously affecting the cellulose or appreciably diminishing the yield. Better results are secured where the final stage of the digestion or cooking is carried out at high temperatures and pressures, as a sub-\ sequent extraction with alkaline li uor then results in a still further diminis ed consumption of the chlorinating agent in the following chlorination treatment. For purposes of illustrating a preferred embodiment of the method, the invention is hereinafter described in connection with the treatment of wood,-and more particularly of hard deciduous wood such as leached chestnut chips from which tannic acid has been extracted.

Referring to the drawings, a conventional chip breaker or hog is indicated at 10 which serves to subdivide the logs or pieces of wood into chips of suitable size, such as a size suitable for boiler fuel. If a supply of chips is available, such as leached chestnut chips, a chip storage may replace the chip breaker. The chips are fed by a conveyor 11' into a feeding hopper 12 which discharges into a digester indicated at 13. This may be a conventional digester, such as a stationary, ro-

tary or tumbling digester, having a feeding opening 14 closed by a removable cover 15 and a conical discharge end 16 provided with a discharge valve 17. A steam supply pipe 18 is provided, which may be connected as shown for a stationary digester, or connected through the trunnions in a rotating or tumbling type of digester. Cooking liquor is supplied from a tank 23 through a pipe 24 controlled by a valve 25.

The chips are subjected in the digester 13 to what is termed an incomplete digestion.

This is so controlled that the chips retainsubstantially their. original form, but may thereafter be readily defibered with properly coordinated mechanical and chemical treatments. This incomplete digestion may vary considerably, depending upon the fibrous material bein treated and the ultimate product desired. is an example of such an incomplete digestion, a so-called semi-chemical cook is hereinafter more fully described. This serves to soften the adhering incrustants, such as lignins, holding the fibers together without dissolving a large proportion of these incrustants and without deleteriously afiecting the cellulose, thereby giving high yields and high strength. Very satisfactory results are secured with a cooking liquor comprising an aqueous solution of an alkali metal sulphite containing a salt of a weakly ionized polybasic acid, such as a mixture of sodium sulphite and sodium bicarbonate. Other alkali metal sulphites, such as potassium sulbite, and other salts of weakly ionized polyasic acids, such as alkali metal carbonates, tartrates, citrates, borates, oxalates, and the like, may be used. 7

' The cook is carried out in stages. In practice, the cover 15 of the digester 13 is removed and chips are fed by the conveyor 11 into the may be positioned at a sufiicient height to permit the liquor to feed in by gravity, or a pump may be used. Steam is then introduced into the mixed mass to raisethe temperature to about 125 C. to 150 C. for a period of time,

, generally about one hour to two hours, to

secure impregnation of the liquor throughout the individual chips. The valve 25 is then opened, and the unabsorbed liquor within the digester is forced back into the tank 23 by ,means of steam pressure existing within the digester. A portion of the liquor is 'retained or absorbed by the chips within the digester. The liquor returned to the tank 23 is partially exhausted by reaction during the impregnation stage. Fresh concentrated make-up liquor is supplied from a tank 27 through pipe 28 to the tank 23 to make up the volume and concentration of the liquor within the tank 23 to provide cooking liquor for a subsequent charge.

The chips with absorbed liquor are then steamed to raise the temperature within the digester above 160 C. and preferably as high as 180 C. to 210 C. or higher, and to raise the pressure to about 160 to 200 pounds per square inch or higher, for a period of time to secure the desired reaction of the liquor with the lignins and other bonding material to secure the desired softening of the chips. According to the length of time and temperature of this reaction stage heating treatment, the characteristics of the cooked material are determined, such as whether it can be easily hydrated or not, its bulkiness and the degree of hardness or softness of the cook. Satisfactory results are secured with a treating time in this reaction stage of about one to four hours.

When the cooking liquor within the digester is maintained approximately neutral still better results are obtained, the lignins being effectively desolved or softened while the cellulose is substantially uninjured. Highly satisfactory results are secured when the pH value of the solution is maintained between 5 and 9. During the .cooking, pyroligneous acids are liberated from the wood which tend to render the cooking liquor acid in character. The presence of the alkali salt of a weakly ionized polybasic acid, such as sodium bicarbon ate, effects the neutralization of these acids as formed. In order to neutralize any alkalinity resulting from hydrolysis of the sodium salts producing caustic soda, an excess of carbon dioxide gas'is preferably present during the cooking operation, this forming carbonic acid within the digester and reactis obtained with steam alone.

- bon dioxide gas under pressure to provide an excess of the gas within the digester during both the impregnation and reaction stages.

The control of the neutrality of the cooking liquor may be easily accomplished by noting the temperature and pressure conditions with in the digester. If steam alone is injected into a digester and other gases or vapors are absent, a definite pressure is obtained at any definite temperature. By the introduction of carbon dioxide gas, a still higher pressure is obtained at any definite temperature than T'Vhen a bicarbonate containing cooking liquor, such as sodium bicarbonate, is used, a certain amount of decomposition of the chemical with the formation of CO gas results, so that the pressure obtained within a digester with such a cooking liquor is due not only to steampres sure but also to false pressure of the carbon dioxide gas resulting from the decomposition of the bicarbonate. By running a series of tests to determine the degree of decomposition of a sodium bicarbonate solution at higher temperatures, a temperature-pressure chart may be plotted which will indicate the pres sure which should be obtained within the did gester at any temperature when bicarbonate is present. In operation, the actual pressure in the digester may be maintained slightly above this calculated pressure for any given temperature by the introduction of excess CO gas through the pipe 30. If the pressure within the di ester falls below the predetermined normal w or any given temperature, manipulation of the valve 31 toward opening position will restore the desired conditions with the digester. Should the actual pressure recorded in the digester rise above predetermined normal for any given temperature, the digester is relieved by allowing some of the gas to escape through the pressure relief valve 32. A control chart may be provided for the digester, and the control of the cooking conditions within the digester effected by proper manipulation of the valves controlling the introduction of steam and carbon dioxide in accordance with variations in pressure from the desired predetermined normal as indicated on the chart for any particular temperature.

The cooked material is discharged from the digester 13 intoa dump tank 35. The

material' at the completion of the cooking is softened but still maintains to a large degree its shape. To facilitate the subsequent hanthe softened material is not shredded 01' but is merely dumped so that :10

pulped at this stage, but is maintained in-- chip form. The mass of softened chips discharged into the dump tank 35 is then washed to remove residual liquor. The washing may be performed by the introduction of wash water through pipe 38 onto the surface of the chips within the dump tank. These chips are supported upon a perforated bottom, which may be a lattice-work as indicated at 36, the washing liquor draining through the lattice-work and escaping to recovery through pipe 37.

The dump tank 35 is provided with means for feeding the softened and drained chips at a controlled rate to a mechanical disintegrator. As illustrated the bottom of the dump tank is provided with an opening 40 located adjacent the periphery of the tank. This opening is closed by a sliding valve 41 during the dumping and washing operations, and is then opened to permit the feeding of softened chips at a controlled rate onto an endless conveyor 42. Positioned within the dump tank is a leach caster, which comprises a centralvertical shaft 45 supported in suitable bearings and driveiuthrough gears 46 and 47 from a drive shaft 48, which in turn is driven at a controlled and variable rate from any suitable source of power. A stirring arm 50 is slidablymounted on the shaft 45 for vertical movement thereon and is keyed to the shaft so as to rotate therewith. The arm carries a plurality of inclined blades or fingers 51 which are so inclined as to move the chips toward the periphery of the tank upon rotation of the shaft 45 and arm 50. The arm 50 is rotatably supported by a thrust bearing 52 carried by a non-rotatable cross beam 53 which is suspended by cables 54 from a winding drum (not shown) which is adapted to be rotated in opposite directions through suitable conventional driving machinery (not shown) at variable speeds to lower or raise the stirring arm 50 in accordance with the level of the chips Within the tank 35, so that the arm 50 operates upon the upper surface of the chips. The rate at which the chips are fed to the periphery of the tank is controlled by the rate of rotation of the shaft 45, or by the rate of lowering of the arm 50, this in turn controlling the rate at which the chips are fed through an opening 39 in the latticework 36 and the aligned opening 40 onto the conveyor 42. v

The conveyor 42 discharges the chips into a receiving hopper 55 feeding into an endless bucket elevator 56, which in turn discharges onto an endless conveyor 57 feeding into an inlet 58 of a rod mill 60. Any suitable type of mechanicaldis'integrator can be .used ,to disintegrate the softened chips at mer type mills, edgerunner mills and the like.

A controlled supply of dilution liquor is ad mitted concomitantly with the softened chips through i a supply pipe 62. The dilution liquor is generally controlled to provide a stock consistency of about 5% to 8% within the rod mill.

In order to reduce the chlorine consumption of the subsequent chlorination, the digested material is subjected to an extraction treatment with a caustic liquor, preferably caustic soda. Very satisfactory results are secured with a cold dilute NaOH solution of a concentration as low as 1 to 1% or even less. This liquor may be maintained at ordinary room temperatures, or may be heated below the boiling point, the cold extraction proving quite satisfactory. The efi'ectiveness of this extraction treatment has been found to vary somewhat with different species of wood. This extraction is preferably carried out during the mechanical disintegration. 1 Thus the digested fibrous material and the alkaline liquor may be added concomitantly and in proportionate quantities by the conveyor 57 and the pipe 02 respectively to the rod mill 60, and the extraction and the mechanical disintegration are' thus carried out very effectively at the same time. The pounding and shredding treatment in the rod mill or other disintegrator provides an agitation of the mixed mass which insures effective penetration of the alkali within the fibrous material whereby highly satisfactory extraction is secured, while at the same time this treatment in the presence of the alkaline liquor gives superior disintegration of the fibrous material.

It is found that when the cooking in the reaction stage is carried to temperatures in excess of 160 (3., then the extraction step effects still further reduction in chlorine consumption in the subsequent chlorination. Very satisfactory results are secured where the temperature in the reaction stage of the cooking israised as hi h as 180 C. to 210 0., or even higher, an a pressure of 160 to 200 pounds per square inch or higher is maintained. Where substantial neutrality of the cooking liquor is maintained, these high temperatures and pressures do not injuriously affect the cellulose and high strength and high yield of the resulting product is nevertheless secured. Reaction of neutral sodium sulphite liquor with the lignins and other incrustants is apparently most effective at temperatures in excess of 160 C. While it has-not been definitely ascertained, it is believed that the 'lignins are in the main not facilitate the subsequent chlorination.

dissolved out by this high temperature cook, but are converted into other compounds which are soluble in dilute NaOH sothat they are readily extracted. Other compounds ma be converted into a stable form such that t ey do not take up as much chlorine to form highly substituted chlorination products during the subsequeiit chlorination. The net result is that a pulp of high yield and high strength is obtained with a mate rially decreased chlorine consumption.

Very satisfactory results are secured with an economy in theoperation in this reaction stage where the temperature is maintained about 160 0., or not materially above, for several hours, and the temperature is then raised to a high point of 180 C. to 210 C. or even higher for a short time, such as about half an hour.

The rod mill comprises an'outer rotary shell 03 which contains therein a plurality of lose parallelly arranged rods extending substantially throughout the length of the shell. The contracted ends 58 and 64 of the shell are supported in suitable bearings (not shown) and the body of the shell is provided with an annular gear 65 which is driven through gearing from a suitable power shaft (not shown). The softened chips are simultaneously fed into the inlet 58 with dilution liquid from pipe 62, and the stock feeds from the inlet 58 to the discharge (it as the casing 63 is rotated tothereby give a thorough pounding, rubbing and shredding treatment to the fibrous material which serves toreduce the softened chips and to hydrate the fibers without objectionable cutting of the fibers, to thereby directly expose the small particles or hard fiber bundles or shives to In disintegrating mills of this character provided with loose or swinging impacting elements, the unreduced bundles or lumps of fibrous material receive substantially the entire action of the movable elements, such as the rods, while the portions that are sufliciently reduced are protected by the lumps against further reduction and cutting action. The rod mill has a certain definite capacity and the fibrous material feeds in until the mill is properly filled, or until the treated stock begins to overflow from the discharge end 64. The discharge from the mill then proceeds in accordance with the rate at which fresh material is fed into the mill, the time of treatment within the rod mill being thereby controlled by the rate of feed.

The material discharged through the end 64 of the rod mill feeds into a stock chest 68 provided with suitable agitating mechanism, such' as driven shaft 69 having agitating blades 70. At this point additional dilution liquid, such as white water, is added through a pipe 71 to reduce the consistency of the it can be readilyv pumfped through conduits, a consistency range 0 about 3% to 5% giving satisfactory results. Stock is withdrawn from the chest 68 through p1pe 72 by a suitable pump such as a centrifugal pump 73, which feeds it through a pipe 74 to the central compartment 75 of a conventional head box 7 6. As shown, the box 76 is divided by part1- tions 77 and 78 into outer compartments 79 and 80 and central compartment 75. I The compartment 79 is connected by pipe 81 with the stock'chest 68, whereby the excess of stock pumped to the head box and overflowing the partition 77 is returned to the stock chest 68. The compartment 80 is connected by pipe 82' to a conventional mixing box 83 The partition 78 is provided with an ad ustable gate or weir 84. which serves to provide for the feeding of a controlled amount of stock to the mixing box 83. The mixing box has a plurality of staggered battles 85 to etlect a thorough mixing of the stock andadditlonal dilution' liquor introduced by a pipe 86, thls serving to further reduce the consistency of the stock to a point most efiective for screemng and filtering, such as about 1% to 2% The stock discharges from the mixmg box 83 through pipe 87 into a conventional coarse screen, illustrated as a rotary screen 90. Th 1s comprises an outer confining caslng 91 within which is rotatably mounted a spaced cylindrical screen 92. The stock feeds from the pipe 87 into the interior of the rotary screen, the meshes of which are sufiiclently large to permit the material which has been sufiic1ently defibered and the dilution liquor to pass therethrough into the outer confining caslng 91 from where it discharges through pipe 93. The larger undefibered particles, lumps and knots which do not pass through the screen are discharged at the end onto a suitable conveyor 94, or otherwise collected, for the purpose of feeding them back into the 1nl.et 58 of the rod mill 60, whereby the taillngs are returned to the system for further reduction.

The screened material discharges from the pipe 93 into a continuous filter mechanism 95 which serves to wash and thicken the treated material. This filter mechanism may be a conventional rotary vacuum filter such as an Oliver filter. This comprises a cylindrical rotary screen 96 divided into compartments of definite suction areas. The screen dips into the stock confined within a tank 97 into which the stock from the pipe 93 discharges. Suction within the compartments of the screen causes the fibrous material to accumulate on the surface of the screen as the water passes therethrough into the suction compartments. As the screen rotates carrying the filtered fibrous mat above the liquid level in the tank, a supply of wash water is directed upon the mat from supply pipes 98. This serves to the stock remove any remaining cooking liquor from the material. As the filter continues to rotate the mat which has thus been washed and through pipe 107 to a conventional head box 108 similar in construction to the head box 76. The overflow pumped to the head box 108 is returned by pipe 109 to the stock chest 102, and a controlled quantityof the stock passes by pipe 110 to the chlorination apparatus where the disintegration of the fibrous material into pulp is completed.

A controlled supply of chlorinating agent such as chlorine water or chlorine gas is introduced into the stream of fibrous material by pipe 111 controlled by valve 112. The stock may be made down to low consistency in chest 102, or the chlorine water may be quite dilute to additionally lower the consistency of the stock such that objectionable temperature rise of the diluted mass in the initial chlorinatipn is avoided. In dilute consistency, the water in which the fibers are suspended apparently serves as a heat-absorbing medium, serving to prevent an objectionable temperature rise of the mass dueto the chlorination, and also serving to dilute hydrochloric acid formed in the reaction, this additionally diminishing objectionable results. Very satisfactory results have been secured with consistencies below 5%.

readily flowed or pumped through conduits or treating chambers. The fibrous mass and chlorinating agent pass together into a mixer 113 which comprises a length of pipe having a spiral baflie 114 therein to create turbulence in the flowing stock stream to mix the chlorinating agent with the mass. The mixed mass then passes into the chlorinating tank or chamber 115 which is constructed of acidproof material such as tile or the like and is divided into a plurality of connected chambers, represented in the drawing by two chambers 116 and 117 divided by a central partition 118 terminating short of the bot tom of the tank. The mixed mass and chlorinating agent flow downwardly through the space 116 and beneath the lower end of the partition 118, and up through the space 117 to the overflow pipe 120.

The tank 115 is constructed of a capacity to accommodate sufficient material to provide the desired reaction time as the stock flows from the inlet tothe outlet. In this manner, a continuous chlorination is eflected as the mass flows along. The amount of chlorinating agent is continuously controlled by the valve 112, preferably in an amount insufficient for complete chlorination. a result,themorereadily-chlorinatedmaterialfirst reacts with the chlorinating agent in a comparatively short time as the mass flows along.-

The amount of chlorinating agent, however, is preferabl Controlled to be as much as will be readily taken up by the fibers in this short treating period, while insuring substantially complete reaction. This initial reaction is rapid, and it has been ascertained that the .reaction of about 85% of the chlorine required for complete chlorination of a given fibrous mass goes to substantial completion in about 15 to 20 minutes. Generally the ad dition of about .to.95% of the chlorine needed for complete chlorination in this first stage with a treating time of about half an hour gives very satisfactory results. v

Various reagents may be used for this first stage, such as chlorine, sodium hypochlorite,

bromine and the like, which for purposes of description are herein termed chlorinating a ents. Chlorine is preferred due to the ease 0 control, efiectiveness and rapidity of reaction, and lesser cost of the chemical. However, the use of ordinary bleach liquor or other calcium compounds at this point is not so'satisfactory, due to the formation of insoluble calcium compounds in the pulp which are not readily washed out in subsequent washing treatments. At this stage, the chlorine may be added in a roughly controlled amount suflicient to effect this initial chlorination, and this is usually done by adding chlorine water of a strength and in an amount to dilute the stock to the desired low consistenply and to preferably provide an amount insu cient for complete chlorination within the limits above mentioned. The addition of chlorine is in practice controlled according to the characteristics of the particular type of fibrous material or, stock being treated, as regards chlorine consumption, rate of reaction,

and the like, and this may be determined for each particular fibrous material by tests.

The overflow outlet 120 from the chlorination chamber 115 discharges into a conventional type of washing apparatus, shown di-. agrammatically-as-a worm-type drum washer. This comprises an acid-proof perforated rotary drum" or screen 123 having an interior ribbon conveyor or spiral 124 and spray pipes 125 for spraying wash water upon the stock. The stock feeds into the interior of one end of the rotary drum and is carried continuously through by the spiral conveyor as it is washed by the sprays and discharges from the other end. A part of the water in the stock drains through the perforated drum into a receiving tank 126 having a discharge pipe 127, so that the stock generally ,discharges from the washer at a'consistency of about 10% to 12%. The short time of treatment in the chlorination chamber coupled with the fact that the free acid formed in the reaction is washed out immediately after chlorination further serves to prevent injury to the fibers. An additional spray pi e 128 is preferably provided to direct an al aline' A discharge 130 from the worm washer feeds to a further thickening device where the stock is dewatered to a consistency of substantially 15% or higher, preferably 20% to 30%, to render it readily permeable to gas. A continuous centrifugal thickener functions very satisfactorily for this purpose, and such a' machine is diagrammatically illustrated herein. This comprises an inner distributing rotor 131 having a spiral flange 132, the rotor being keyed to a shaft 133 driven by a motor134, and a second rotor or perforated filtering screen 135 carried by a sleeve 136 rotatab y mounted upon shaft 133.. and also driven from motor 134 through gearing (not shown) at a speed which is preferably sli htly less than the speed of the rotor 131. The outer screen is surrounded by a stationary annular casing or trough 138. The discharge 130 continuously feeds the stock into the space between the inner rotor 131 and the out: er perforated filtering screen 135, where it is carried through the machine by the spiral flange 132 while being subjected to such centrifugal force as to,causea portion of the retained water in the mass to pass through the filtering screen 135 into the trough 138, from where the filtrate is removed by a pipe 139. Other well known types, of continuous thickeners may be used for this purpose, such as rotary vacuum'filters or cylindrical thickeners with pressure rolls to regulate the water content of the stock.

The dewatered stock discharged from the of more drastic action, in which a high chlorine concentration is effective in the fibrous mass, the chlorine gas reacts'with the more resistant ligneous matter with consequent resolution of the shives or other undefibered material, this permitting the successful resolution of hard wood into satisfactory pulp. A t the same time the strength of the fibers. is

maintained, and other high quality characteristics are secured. During such reaction,

line solutions, or which are of such character as to color and other characteristics as to be subsequently unobjectionable and ineifective to lower the quality of the resulting pulp.

As shown diagrammatically herein, the elevator 142 discharges into a hopper 145 which feeds into a screw conveyor 146 having an opening 147 on the lower side thereof opposite the open upper end of the tower 143. Stock feeds through the opening 147 into the upper end of the tower 143 as needed to maintam the tower full of stock, the surplus stock handld by the screw conveyor 146 being d1s-' charged at the end 148 and returned to the source of supply. The tower 143 is provided with an inlet 150 for the introduction of a controlled supply of chlorine gas, and controlled outlets 151 and 152 for the discharge of gas. The gas discharging from the tower which contains some free chlorine is preferably passed to recovery apparatus (not shown), such as a water absorption system, where chlorine water is formed which may be used in the first stage of the chlorination. Water or other slushing liquid is introduced adjacent the base of the tower at 154 to dilute and slush out the pulp through the water sealed discharge 155 formed between the lower end 156 of the shell of the tower and a base 157, the stock passing into an annular trough 158. The stock passes from the upper end to the lower end of the tower by gravity in accordance with the rate at which it is slushed out at the bottom, thereby providing a continuous travel of dewatered stock through a controlled and maintainedatmosphere of chlorine gas which thoroughly permeates the mass fibers and effects intimate contact therewith. Generally a treating period of 15 to 30 minutes in this second stage is satisfactory, although a longer period may be used.

The chlorinated stock slushed out at the base of the tower 143 is discharged, with the aid of additional slashing liquid introduced into the trough 158 by a pipe 160, through a pipe 161 into a solvent tank 162. Here it is mixed with a controlled quantity of alkali continuously supplied from a pipe 163 having a control valve 164 for the purpose of dissolving out reaction products of the chlorination. The alkaline liquor washed out of the extracted fibrous material prior to chlorination by the Oliver filter 95 is quite satisfactory for this purpose, and such liquor may be supplied directly to the pipe 163. The tank 162 is constructed to effect a continuous and uniform treatment of the fibrous material secure a thorough mixing of the material" with the solvent alkali. For this purpose the tank is providedwith a plurality of staggered bafiies 166 which provides. circuitous path for the flow of material from the inlet 167 to the discharge 168 connected to the suction side of a pump 169. The first compartment of the tank 162 ispreferably provided with suitable agitating mechanism such as a driven shaft 170 having a plurality of rotary stirring arms 171. The capacity of the tank 162 is such that the treated material is allowed to remain about halfan hour therein, thisgiving sufficient time for soluble reaction products of the chlorination to be dissolved. Any suitable alkali may be used for this purpose, dilute cold solutions of caustic soda, sodium carbonate or sodium sulphite giving very satisfactory results.

The pump 169 feeds the diluted stock through a pipe 175 to a continuous filterinechanism indicated generally at 176 which may be a conventional rotary vacuum filter, such as an Oliver filter, similar in construction to the filter 95. The dissolved reaction products of the chorination and the excess alkaline liquor are washed out of the stock by wash Water from spray pipes 177, and the filtered and thickened material is removed from the surface of the filter by a scraper 178 into a chute 179 which discharges into the first tank 180 of a bleacher which is preferably of the continuous type. The alkaline liquor and wash water drawn rior of the rotary screen 17 6 are discharged through a central pipe 182, and a portion of this alkaline liquor may be supplied to the supply pipe 128 of the Worm washer.

.ny suitable construction of continuous bleacher may be used. As shown, three connected tanks 180, 183 and 184, each having a rotary shaft 185 provided with stirring arms 186, are provided. The tanks are arranged at successively lower elevations and the bottom of a preceding tank is connected to the upper end of a succeeding tank by a pipe connection 187. Each connection 187 has its highest point located below the level of the stock in the preceding tank, whereby a head is effective to secure a flow through the pipe. The capacity of the tanks is such as to insure suffiby suction into. the intecient time for the completion of the final isl to produce a pulp having a high white color.

The bleached pulp stock continuously discharged from the last tank 184 through pipe 190 is forced by av pump 191 to a rotary vacuum filter indicated generally at 192, similar in construction -to the filter 176, where the disintegrated fibrous material discharged from the rod mill is introduced into a hopper 2000f an extraction tank 201 constructed similarly to the solvent tank 162. A pipe 202 having a control valve 203 is provided to ad mit controlled quantities of alkaline liquor into the extraction tank along with the fibrous material. The tank 201 is provided with staggered baflles 204 and an agitator 205 for the first compartment. The consistency of the stock is made down to less than i 5% at this point, and a pump 7 3' feeds the extracted stock through a pipe 74 to a conventional head box in the manner in whlch the stock is fed from the stock chest 68 in Fig. 1. Or if desired, alkaline liquor maybe introduced into the rod mill 60 by the pipe 62' to secure extraction and mechanical disintegration in the presence of alkali, and the extraction then completed in the tank 201, further alkaline liquor or dilution liquor being introduced by the pipe 202. The constructionof the apparatus and the operationis otherwise the same as that of Fig. 1.

In order to conserve as by-products of this pulping treatment the ligneous and other incrustant material dissolved out of the fibrous material, thereby efiecting a further economy in the process, this organic material is preferably separated from the solvent liquor. Where a mild substantially neutral cook is used as in the incomplete digestion above described, these organic materials are not converted into objectionable reaction products which are subsequently ditficult to handleas is the casein the conventional practice where a drastic cooking treatment with strong cooking liquor is used, but these materials-may be readily separated from the cooking liquor and from the extraction or solvent liquor.

Thus the cooking liquor drained from the cooked material through the pipe 37 may be treated to recover ligneous by-products therefrom. The combined extraction and alkali solvent liquor removed from the fibrous material by the filter 176 may be also treated to recover these organic materials as byproducts. The spent cooking liquor and the combined extraction and alkali solvent liquor are preferably separately treated, this progressive extraction of the recovered organic material being advantageous in that higher quality by-products are generally secured from-the extraction and solvent liquor than from the cooking liquor. 'Thisorganic material readily admits of separation into two fractions, one of which appears to be-phenol c 1n character and is precipitated by soluble carbonates from an alkaline solution, and another fraction which is by acids.

The cooking and chlorination treatments as carrled out in accordancewith this invention are so controlled. or limited in their effects upon the cellulose contentv of the fibrous material, that even the 'less resistant beta and gamma celluloses are substantially un1n ured, and only small amounts are lost by solut on in contradistinction to the conventional pulping methods heretofore used.

hydrolyzed or converted into oxycellulose. The result is that a novel and superior white pulp product having unusually advantageous characteristics with a high yield is obtained. In actual tests using chestnut and gum, this pulp product has been found to contain a cellulose contenit in excess of 20% of beta and gamma cel ulose and less than 80% of alpha cellulose. The average strength is more than 50% higher than that of paper formed from conventional soda pulp from the same species of wood, often bein twice as strong, and is superior to that 0% paper formed from strong sulphite pulp. The bleached product is of the highest color grade. The pulp is characterized by high felting and clay carrying qualities, and it may be loaded to contain as much as 40% of filler without dusting. Paper formed from the product is free of the objectionable fuzziness, which is a characteristicof paper formed from soda pulp. The combination of high strength, good color and exceptional clay. carrying qualities makes the product highly satisfactory for use in printing paper, such as book paper. The pulp is free, that is water drains rapidly through a mat undergoing formation on a forming wire, and is easily hydrated, which makes the pulp especially suitable for other types of highgrade paper, such as bonds and writing paper, parchment, glassine, waxing, and the like. The yield of unbleached pulp generally averages between 75% to 80% on the dry weight of the wood, while the yield of bleached pulp generally averages over on the dry weight of the wood. This is an average increased yield of over 30% as compared to the soda process, and is materially higher than average yields obtained by the sulphite and kraft processes.

The following is a typical example of apulping treatment carried out in accordance precipitated 7 The alpha cellulose content is not materially 1pounds of sodium bicarbonate (both calcuated, as sodium carbonate) in suflicient water to provide a concentration of about 8% to 12% sodium sulphite and 3% to 5% sodium bicarbonate, is added to the digester. The wood is preferably steamed for about half an hour before the cookin liquor is added. The charge is then broug t up to approximately 125 C. with steam, thecooking be ing continued at around this temperature for approximately two hours. The control of the neutrality of the cooking liquor is of fected by the introduction of carbon dioxide gas through the pipe 30, or the relief of excess pressure through the pipe 32. The valve 25 is then opened and the liquor in the digester is blown back into the receivlng tank '23 where fresh liquor is added from tank 27 to bring it up to strength and volume for the treatment of a subsequent charge.

The chips impregnated with the liquor are then steamed until the temperature is brought up to about 185 C. or higher, an ex cess of carbon dioxide gas being maintained. This second stage of the cooking is generally carried on from one to four hours. The cooked chips are then dumped into the dump tank 35 and washed, the plug valve fpr the outlet being closed. The plug valve is then opened and the shaft and the leach caster driven to feed the softened chips at a controlled rate to the rod mill 60. With a mill having a shell approximately twelve feet long and six feet in diameter and conta' about 40,000 pounds of rods, a rate of feeding of the chips diluted to a consistency of 5% to 8% to give a controlled output of about thirteen tons to eighteen tons of rod milled stock in twenty-four hours is quite satisfactory. The dilution in the rod mill is preferably effected with a cold dilute NaOH solution of a concentration ofapproximately one-half per cent. The disintegrated material is then diluted, screened to remove undesirable lumps and knots','filtered, and then furtherdiluted forthefirststagechlorination.

Chlorine Water containing approximately to 90% of the chlorine required for complete chlorination of the pulp is used. The chlorine is added to the stock in the form of solution in water containing approximately 2% to 4% chlorine or is added directly as chlorine gas. In the former case the fibrous material is made down to a consistency of about 4% to 6%, the addition of the chlorine water bringing the consistency to about 1% to 4%. In. the latter case the consistency of the material is made down initially to about 2% or even less. The rate of flow through the chlorination chamber 115 is controlled to give a treating time of about half an hour.

Ibo chlorinated stock is washed and given v chlorine gas Both stages of on at ordinary room temperatures. The chlorinated stock is then introduced into the' alkali solvent tank 162 with a sufficient quantity of cold .1% NaOH solution to render the mass distinctly alkaline and is agitated and steeped therein for about half an hour. After'washing and making down to about 5% material is introduced into the bleacher with a quantity of hypochlorite liquor suificient to bring the consistency to about 4% to 5% andto provide about 1% chlorine on the dry weight of the pulp. The flow of stock through the bleacher is controlled to provide a treating time of about one hour or more. A preliminary high density bleach may be given, if desired, before the stock is diluted. The bleached pulp is then washed and thickened and dropped to a stock chest where it is ready for use in the manufacture of highgrade paper.

While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In the manufacture of pulp from hrous material, the method which compris s subjecting the fibrous material to digestion with substantially non-acidchemical under such conditions of treatment that the fibrous material is only partially defibered, then extracting the digested material with alkaline liquor to efl'ectpartial removal of chlorine consuming constituents while leaving a substantial proportion of the non-fibrous constituents in the mass and without effectin complete pulping thereof, and further disin tegrating the extracted material to pulp by treatment with a chlorinating agent.

2. In the manufacture of pulp from hard deciduous wood, such as chestnut, oak, gum, and the like, the method which comprises cooking the woody fibrous material with a cooking liquor including an alkali metal sulphite and the salt of a weakly ionized polyhasic acid to eflect a partial defibering of the fibrous material, extracting the cooked material with alkaline liquor at temperatures below the boiling point of the liquor to effect partial removal of chlorine consuming constituents while leaving a substantial proporconsistency, the

material to small pieces and remove chlorine consuming constituents while leaving a substantial proportion of unreduced fiber bundles and shives as well as non-fibrous con- .stituents in the mass, and then further disintegrating the extracted material to pulp by treatment with a chlorinating agent.

4. In the manufacture of pulp from fibrous material, the method which comprises subjecting the fibrous material to dlgestion wlth chemical under such conditions of temperature and pressure and of concentration and character of chemical thatthe fibrous material is only partially defibered, rod milling the incompletely defibered material in the presence of alkaline liquor to further disintegrate the same and effect extraction thereof but insuflicient to effect complete pulping thereof and leaving a substantial proportion of unreduced fiber bundles and shives as well 'as non-fibrous constituents in the mass, and then further disintegrating the extracted material to pulp by treatment with a chlorinating agent.

5. In the manufacture of pulp from fibrous material, the method which comprises subjecting the fibrous material to digestion with chemical under such conditions of temperature and pressure and of concentration and characterofchemicalthatthe fibrous material is only partially defibered, removing cooking liquor from the digested material, then further disintegrating the material to pulp by treatment with a chlorinating agent, treating the chlorinated material with solvent liquor to dissolve out reaction products of the chlorination, removing solvent liquor from the treated material, and treating the removed solvent liquor to recover lignins and bonding materials dissolved therein.

6. In the manufacture of pulp from fibrous material, the method which comprises subjecting the fibrous material to digestion with chemical under such conditions of temperature and pressure and of concentration and character of chemical that the fibrous material is only partially defibered, then extracting the digested material with alkaline liquor, separating the fibrous material from the extracting liquor, further disintegrating the fibrous material to pulp by treatment with a chlorinating agent, admixing the chlorinated material and extracting liquor separated from the fibrous material after the extractin ste to dissolve out reaction products of the ch orination, and then separating the chlorinated material from this liquor.

7. In the manufacture of ulp from fibrous material, the method which comprises subjecting the fibrous material to the action of a cooking liquor under such conditions of temperature and pressure and of concentration and character of chemical that the fibrous material is only softened without substantial pulping thereof, then treatin the softened material with an extracting liquor in the cold or at temperatures substantially below the boiling point of the extracting liquor to effect partial removal of chlorine consuming constituents while leaving a sub- Stantial proportion of fiber bundles and shives as well as non-fibrous constituents in the mass, and further disintegrating the extracted material to pulp by treatment with a chlorinating agent. 8. In the manufacture of pulp from hard wood such as gum and the like, the method which comprises cooking at temperatures in excess of 170? C. the woody-fibrous material with a cooking liquor containing an alkali metal sulfite andr the alkali metal salt of a weakly ionized polybasic acid so that the fibrous material is softened without substantial pulping thereof, mechanically disintegrating the softened material in the presence of an alkaline liquor to effect further extraction but sufiicient to effect only a partial pulping thereof, further disintegrating the mechanically treated material to pulp by treatment with a chlorinating agent, dissolvin out reaction products of the chlorination, and bleaching the resultant pulp to produce a pulp suitable for the manufacture of high grade papers, such as for printing, writing and the like. i

9. In the manufacture of pulp from fibrous material, the method which comprises cooking the fibrous material at high temperatures in excess of 170 C. and at high pressures with a chemical cooking liquor containing a normal alkali metal sulfite and the alkali metal salt of a weakly ionized polybasic acid in proportions such that the fibrous material is softened without being pulped, the treatment at high temperatures and pressures being such as to eifect a substantial reduction in the ability of the fibrous material to consume chlorine, then further disintegrating the incompletely defibered material to pulp by treatment with a chlorinating agent, dissolving out reaction products of the chlorination, and bleaching the resultant pulp.

In testimony whereof we hereto afiix our signatures.

JOHN TRAQUAIR. FRANCIS G. RAWLING. 

